The present invention relates to a suspension system for a vehicle axle with at least one hydraulic suspension cylinder, which comprises a chamber, with the chamber being connected to a hydraulic accumulator and capable to be optionally connected via shifting means to a pressure source and a pressure release, with a shut-off valve being arranged between the chamber and the accumulator, and with the suspension system comprising a detection device for detecting a pressure difference between the chamber and the accumulator.
Hydraulic and/or hydro-pneumatic axle suspension systems have been used for quite some time in vehicle construction of passenger vehicles; however they are also used increasingly in agricultural machines, particularly in modern tractors with a front axle suspension. Due to the different operating situations of agricultural machines with widely fluctuating axle loads such front axle suspensions are equipped with a level control and an adjustment of the intensity of the suspension. Furthermore, in certain operating conditions, for example when hoisting heavy loads via front loaders, a blockage of the front axle suspension must be possible.
A suspension system is described for example in the publication EP 2730438 A1 for an articulately supported vehicle axle with at least one hydraulic suspension cylinder that can be arranged between the vehicle axle and a carrying vehicle structure, which shows two chambers, which are respectively connected to different hydraulic accumulators.
Blocking such a suspension device can occur here in that a shut-off valve is arranged between the chamber and the hydraulic accumulator. If the hydraulic connection between the chamber and the accumulator is interrupted, here the elastic motion of the hydraulic cylinder is blocked by the incompressibility of the hydraulic medium used.
A disadvantage of such a blocking of the suspension system is the fact that upon release, thus when opening an appropriate shut-off valve between the chamber of the hydraulic cylinder and the accumulator, a compensating motion of the suspension occurs, depending on the load presently applied to the front axle, which can only be compensated to an insufficient extent by an automatic level control.
A hydro-pneumatic suspension system for wheel bearings is known from DE 32 26 452 C2, in which via a shut-off valve the accumulators of the suspension cylinder can be separated from the hydraulic accumulator connected via a connection line in order to block the suspension. A cross-over valve is installed in the connection line between the hydraulic accumulator and the suspension cylinder, which the hydraulic accumulator optionally connects to the connection line or to the pressure compensation valve. When the suspension is blocked and the vehicle is then to be returned to a suspended condition here the hydraulic accumulator is connected via the cross-over valve to the pressure compensation valve and the shut-off valve to the suspension cylinder is opened. Now a pressure difference—switch, connected to the connection line and the hydraulic accumulator, determines any potentially given pressure difference between the hydraulic accumulator and the hydraulic cylinder and opens the pressure compensation valve for such a period until the pressure in the hydraulic accumulator is adjusted to the one in the suspension cylinder. Subsequently the hydraulic accumulator is connected via the cross-over valve to the suspension cylinder. Here, the complexity of the hydraulic circuit and the successive addressing of several valves is disadvantageous, which renders the suspension system susceptible to malfunction. Additionally, the shut-off valve must be opened in case of any pressure difference given, which can also lead to a compensating motion based on a certain (although minor) compressibility of the hydraulic fluid in the suspension cylinder and the supply lines.